Mobile machines, especially off-road construction and agricultural machines, use hydraulic systems to power the machine implements as well as any attachments which may be temporarily used with such machines. Hydraulic power and the pumps, motors and valves used to deliver such power are ideal for these functions. Hydraulic power provides excellent control and the machine designer is not limited by the constraints which would otherwise be imposed by rigid mechanical drive lines.
Some machines of the foregoing type use a loader bucket or other type of work implement which may be raised well above the ground and held there indefinitely by maintaining the hydraulic valve control spools associated with such implement in centered position(s). A particular type of construction machine which uses are loader bucket and other work implements is known as a skid-steer loader.
(A skid-steer loader is so named because none of the wheels are capable of being pivot-steered. Rather, steering is by powering the left-side wheels and the right-side wheels at different rotation speeds. Some wheel skidding results.)
A skid-steer loader is configured in such a way that an operator must gain access to the operator's seat over the front of the machine. There is no barrier preventing such access.
Because of machine geometry, the absence of a compartment front barrier is necessary to permit the operator to easily see the work being performed. And if the bucket is raised, such operator may walk or crawl under it when boarding or leaving the machine.
Designers of such machines (as well as those designing other types of construction machines) work hard to prevent the implement-holding valve spools from being moved out of their neutral or implement-holding positions until intentionally moved therefrom. A way of doing so is to apply some sort of external locking mechanism to the mechanical linkage extending between the operator's lever and the valve spool itself.
But operators have demonstrated that linkage-attached external locking mechanisms can be defeated, either intentionally or by simply failing to properly maintain such mechanisms. Sooner or later, such mechanisms are damaged in use or wear out and need repair.
An improved lockout mechanism which overcomes some of the problems and shortcomings of the prior art would be an important advance in the art.